Imaging of the power distribution of a circular oversized waveguide with a Josephson cantilever at 762 GHz

The transmission of FIR (far-infrared) radiation with a Gaussian intensity profile through oversized hollow metal waveguides and a quasi-optic HDPE lens system has been studied to determine the optimal conditions for analysis of THz antennas. We present applications of our scanning THz electronics prober STEP. As a scanning sensor we employ a Josephson junction from the high-temperature superconductor YBa2Cu3O7 on a vibrating cantilever prepared from a LaAlO3 bicrystal. This superconducting detector is cooled to a temperature of about 50 K by a cryocooler and the waveguides under investigation stay at room temperature. Based on this set-up in a vacuum chamber we investigate the microwave power density at 762 GHz with high spatial resolution far below the corresponding wavelengths. Measurements have shown that the multimodal radiation distribution in an oversized waveguide is not favorable for the analysis of THz antennas.